Curable Compositions and Membranes

ABSTRACT

A curable composition comprising:
     (i) 2.5 to 50 wt % crosslinker comprising at least two acrylamide groups;   (ii) 12 to 65 wt % curable ionic compound comprising an ethylenically unsaturated group and a cationic group;   (iii) 10 to 70 wt % solvent; and   (iv) 0 to 10 wt % of free radical initiator; and   (v) non-curable salt;
 
wherein the molar ratio of (i):(ii) is &gt;0.10.
   

     The compositions are useful for preparing ion exchange membranes.

RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.13/516,429, filed Jun. 15, 2012 which is a continuation of PCTApplication number PCT/GB2010/052063, filed Dec. 9, 2010, which claimspriority to GB Patent Application number 0921951.0, filed Dec. 16, 2009;each of which are hereby incorporated by reference in their entiretiesfor all purposes.

This invention relates to curable compositions, to their use in thepreparation of membranes and to the use of such membranes in ionexchange processes.

Ion exchange membranes are useful in a number of applications, includingelectrodeionisation (EDI), continuous electrodeionisation (CEDI),electrodialysis (ED), electrodialysis reversal (EDR) and capacitivedeionisation used in e.g. flow through capacitors (FTC) for thepurification of water, Donnan or diffusion dialysis (DD) for e.g.fluoride removal or the recovery of acids, pervaporation for dehydrationof organic solvents, fuel cells, electrolysis (EL) of water or forchlor-alkali production, and reverse electrodialysis (RED) whereelectricity is generated from two streams differing in saltconcentration separated by an ion-permeable membrane.

Electrodeionization (EDI) is a water treatment process wherein ions areremoved from aqueous liquids using a membrane and an electricalpotential to effect ion transport. It differs from other waterpurification technologies, such as conventional ion exchange, in that itis does not require the use of chemicals such as acids or caustic soda.EDI can be used to produce ultra pure water.

Electrodialysis (ED) and Electrodialysis Reversal (EDR) areelectrochemical separation processes that remove ions and other chargedspecies from water and other fluids. ED and EDR use small quantities ofelectricity to transport these species through membranes composed of ionexchange material to create separate purified and concentrated streams.Ions are transferred through the membranes by means of direct current(DC) voltage and are removed from the feed fluid as the current drivesthe ions through the membranes to desalinate the process stream. ED andEDR are suitable techniques for producing drinking water. Ion exchangemembranes are also used in Zero Discharge Desalination (ZDD).

A membrane electrode assembly (MEA) appears suitable for a variety ofapplications such as electrolysis, sensors and especially fuel cells.

A flow through capacitor (FTC) is an efficient means of chemical-freeTotal Dissolved Solids (TDS) reduction using electrically charged carbonelectrodes to remove ions.

One of the important problems in the production of ion exchangemembranes is how to provide thin membranes with minimal defects.Desirably the membranes have good permselectivity and low electricalresistance. Additionally the membranes are desired to be strong, whileat the same time being flexible. Flexibility is required for membraneswhich are to be wound into tight circumferential structures. Themembranes also need to retain their physical integrity over an extendedperiod of time. Desirably the method used to prepare the membranes doesnot result in excessive curl. It is also desirable for the membranes tobe resistant to the chemicals that they can come into contact with, e.g.resistant to hydrolysis.

Membrane users require the lowest prices available, which meansproduction processes for the membranes are ideally inexpensive and themembranes should be easily capable of mass production.

U.S. Pat. No. 5,037,858 describes the preparation of anion selectivemembranes from concentrated solutions of N,N′-methylenebisacrylamide athigh pH. The pH of the composition used in Example 1 is about 13.5 andit is free from non-curable salts.

US 2004/0203149 describes composite materials comprising supportedmacroporous gels. In Example 1 a composition comprising a crosslinker(N,N′-methylenebisacrylamide crosslinker), a curable ionic compound((3-acrylamidopropane) trimethylammonium chloride), solvent and aphotoinitiator is crosslinked to form a macroporous gel. The gel isdescribed as being mechanically very weak. The composition was free fromnon-curable salts.

The present invention seeks to provide compositions suitable for use inthe preparation of membranes, in addition to rapid processes forpreparing the membranes and the membranes prepared by the processes andtheir uses.

According to a first aspect of the present invention there is provided acurable composition comprising:

-   (i) 2.5 to 50 wt % crosslinker comprising at least two acrylamide    groups;-   (ii) 12 to 65 wt % curable ionic compound comprising an    ethylenically unsaturated group and an cationic group; and-   (iii) 10 to 70 wt % solvent;-   (iv) 0 to 10 wt % of free radical initiator; and-   (v) non-curable salt;    wherein the molar ratio of (i):(ii) is >0.10.

The compositions of the present invention have good storage stabilityand membranes produced therefrom are also have good permselectivity andresistance to hydrolysis, even under alkaline conditions. This storagestability is particularly useful for the continuous production ofmembranes where large storage tanks of the composition can be at theproduction line for some time, or in storage waiting to replace a nearlyspent tank. Additionally the compositions have a low tendency to corrodemembrane production equipment such as tanks and piping. The burststrength of many of the membranes was also good.

In one embodiment the composition has a pH of 1 to 12, more preferably1.5 to 11, especially 2 to 10, more especially 3 to 9, particularly 4 to8, e.g. 4 to 5 or 5 to 7. In another embodiment the composition does nothave a pH of 1 to 12.

In one embodiment the composition is free from free radical initiatorsor further comprises 0.005 to 10 wt % of photoinitiator.

The crosslinker is preferably present in the composition in an amount of3 to 45 wt %, more preferably 4 to 35 wt % and especially 5 to 25 or 35wt %. A relatively high crosslinker content generally results in a highpermselectivity with a high electrical resistance while for a relativelylow crosslinker content the formed membrane structure is more openresulting in a somewhat lower permselectivity. A relatively lowcrosslinker content allows for a higher content of curable ioniccompounds and a higher degree of swelling both of which can be usefulfor obtaining a membrane having low electrical resistance. The ratio ofcrosslinker/curable ionic compound is selected depending on the desiredproperties for the resulting membrane which in turn depend on theintended use of the membrane.

When a membrane having low electrical resistance is desired, the amountof curable ionic monomer used in the composition is preferably high,while the amount of crosslinker will be reduced in order to accommodatethe higher amount of curable ionic monomer. Thus to prepare membraneshaving low electrical resistance the preferred crosslinker content is 4to 20 wt %, more preferably 6 to 18 wt %, especially 7 to 15 wt %, moreespecially about 10 wt %. With this amount of crosslinker one can stillobtain a reasonably strong membrane with a good permselectivity withoutexcessive swelling. When a membrane having very high permselectivity isdesired the amount of crosslinker present in the composition willgenerally be chosen higher, preferably in an amount of 8 to 48 wt %,more preferably from 10 to 35 wt %, e.g. of 12 to 30 wt %.

The crosslinker preferably has two or three acrylamide groups, morepreferably two acrylamide groups.

The molecular weight of the crosslinker preferably satisfies theequation:

(Y×m)>molecular weight of the crosslinker

wherein m is the number of acrylamide groups in the crosslinker; and

Y is 120, preferably 105, more preferably 90 and especially 85 or 77.

The lower values of Y mentioned above are preferred because theresultant crosslinkers crosslink more efficiently than when Y is higher.Furthermore, crosslinkers having the lower values of Y mentioned abovehave lower molecular weights, leaving room for higher amounts of curableionic compound and thereby achieving a lower electrical resistance forthe same level of crosslinking and permselectivity.

The crosslinker is preferably of the Formula (1):

wherein:

-   -   R₁ and R₂ are each independently H or methyl;    -   R₃ and R₄ are each independently H, alkyl, R₃ and R₄ together        with the N groups to which they are attached and Y form an        optionally substituted 6- or 7-membered ring; and        -   Y is an optionally substituted and optionally interrupted            alkylene group.

When R₃ or R₄ is alkyl it is preferably C₁₋₄-alkyl.

When R₃ and R₄ together with the N groups to which they are attached andY form an optionally substituted 6- or 7-membered ring they preferablyform a piperazine, homopiperazine or triazine ring.

The optional interruptions which may be present in Y are preferablyether or, more preferably, amino groups. Y is preferably of the formula—(C_(n)H_(2n))— wherein n is 1, 2 or 3.

As Examples of suitable crosslinkers there may be mentionedN,N′-methylene bis(meth) acrylamide, N,N′-ethylenebis(meth)acrylamide,N,N′-propylenebis(meth)acrylamide, N,N′-butylenebis(meth)acrylamide,N,N′-(1,2-dihydroxyethylene) bis-(meth)acrylamide, 1,4-diacryoylpiperazine, 1,4-bis(acryloyl)homopiperazine,triacryloyl-tris(2-aminoethyl)amine, triacroyl diethylene triamine,tetra acryloyl triethylene tetramine,1,3,5-triacryloylhexahydro-1,3,5-triazine and/or1,3,5-trimethacryloylhexahydro-1,3,5-triazine. The term ‘(meth)’ is anabbreviation meaning that the ‘meth’ is optional, e.g. N,N′-methylenebis(meth) acrylamide is an abbreviation for N,N′-methylene bisacrylamide and N,N′-methylene bis methacrylamide.

More preferably R₃ and R₄ are both H and Y is an optionally substitutedC₁₋₃-alkylene group or an optionally substituted—(C₁₋₃-alkylene-N(R₅)—C₁₋₃-alkylene)- group wherein R₅ is H orC₁₋₄-alkyl. Especially preferred crosslinkers are N,N′-methylenebis(meth) acrylamide, N,N′-ethylenebis(meth)acrylamide,N,N′-propylenebis(meth)acrylamide, N,N′-(1,2-dihydroxyethylene)bis-(meth)acrylamide, triacryloyl-tris(2-aminoethyl)amine and triacroyldiethylene triamine.

The presence of non-curable salts in the composition can help todissolve poorly soluble crosslinkers and provide surprisingly stablecompositions, even with poorly soluble crosslinkers such asN,N′-methylene bis(meth) acrylamide.

The non-curable salt can be any salt which is not capable of forming acovalent bond with the crosslinker under the conditions used to cure thecomposition. Typically the non-curable salt comprises an anionic groupderived from an acid (especially an inorganic acid) and a cationic group(especially and inorganic cationic group). The non-curable saltpreferably has a solubility in water at 25° C. of at least 250 g/L, morepreferably at least 400 g/L. Preferred non-curable salts are inorganicsalts, for example inorganic lithium, sodium, potassium, ammonium,magnesium and calcium salts and mixtures comprising two or more suchsalts.

In one embodiment the curable composition is free from lithium andcalcium salts. In another embodiment the curable composition comprises alithium and/or calcium salt.

Preferred non-curable salts include lithium chloride, lithium bromide,lithium nitrate, lithium iodide, lithium chlorate, lithium thiocyanate,lithium perchlorate, lithium tetrafluoroborate, lithiumhexafluorophosphate, lithium hexafluoroarsenate, ammonium thiocyanate,ammonium chloride, ammonium iodide, ammonium nitrate, sodium chloride,sodium bromide, sodium nitrate, sodium thiocyanate, calcium nitrate,calcium thiocyanate, calcium bromide, calcium chlorate, calciumperchlorate, calcium iodide, calcium tetrafluoroborate, calciumhexafluorophosphate, calcium hexafluoroarsenate, magnesium chloride,magnesium bromide, magnesium nitrate, magnesium thiocyanate, potassiumthiocyanate, potassium chlorate, and mixtures comprising two or moresuch salts. Most preferred are lithium chloride, lithium bromide,lithium nitrate, ammonium nitrate, sodium nitrate, calcium nitrate andmixtures comprising two or more such salts.

The non-curable salts preferably comprise a chaotropic anion (i.e.weakly hydrated anion), while the cation is preferably kosmotropic. Thepreferred chaotropic anions are those low in the Hofmeister series ascan be experimentally determined by the order by their elution rate froma packed column comprising epichlorohydrin crosslinked dextran gel inbeaded form (e.g. Sephadex® G-10) as described in detail in J. Biol.Chem., 261, 12477-12485 (1986). Preferred chaotropic anions are thosethat elute slower than or equal to chloride, e.g. thiocyanate, chlorate,perchlorate, chlorite, iodide, bromide, nitrate, chloride and nitrite.The anion preferably is other than sulphate, sulphite, phosphate andfluoride.

The non-curable salt preferably has a relatively low molecular weight(e.g. below 200, more preferably below 150, especially below 110, moreespecially below 90, even more especially below 70. Any waters ofcrystallisation, when present, are not taken into account whencalculating the molecular weight of the non-curable salt.

The curable composition preferably comprises 2 to 50 wt %, morepreferably 2 to 30 wt % non-curable salt. Thus in a preferred embodimentthe composition comprises the above-specified number of parts of (i),(iii) and (iv), 20 to 65 wt % of component (ii) and 2 to 30 wt % ofcomponent (v).

In many cases the presence of the non-curable salt in the compositioncan also improve the permselectivity of membranes made therefrom.

When the crosslinker has low solubility in the solvent (e.g. asolubility of below 2 wt %, the composition preferably comprises thenon-curable salt in an amount of 3 to 40 wt %, more preferably 4 to 30wt %, especially 7 to 25 wt %, e.g. about 10 wt %, or 15 to 35 wt %. Thepreferred amount depends to some extent on the molecular weight of thenon-curable salt and the amount of crosslinker present in thecomposition.

Preferably the ratio of the number of moles of cations being part of thenon-curable salt to the total number of moles of (meth)acrylamide bondsin the composition (including the crosslinker and optionally othercurable monomers) is 0.3 to 1.1, more preferably 0.4 to 1.05, especially0.7 to 1.02, e.g. about 0.9. Surprisingly the presence of thenon-curable salt can provide the composition with advantages even whenthe crosslinker has good solubility in the solvent, e.g. improvedpermselectivity and a more robust membrane.

Preferably the crosslinker has a solubility of at least 2 wt % in a 10wt % LiNO₃ solution in water at 20° C.

The curable ionic compound is preferably present in the composition inan amount of 20 or 25 to 65 wt %, more preferably 35 to 60 wt %,especially 40 to 57 wt % and more especially 45 to 55 wt %. In generalthe amount of curable ionic compound is as high as possible to maximisethe electrical charge density in the membrane.

Preferably the molar ratio of component (i):(ii) is at least 0.15, morepreferably at least 0.2, especially at least 0.25. In one embodiment themolar ratio of component (i):(ii) is preferably below 5.0, morepreferably below 4.0, especially below 1.5, more especially below 1.0 Inanother embodiment the molar ratio of component (i):(ii) is preferablybelow 1.5, more preferably below 1.0, especially below 0.7, moreespecially below 0.5. Preferred curable ionic compounds comprise aquaternary ammonium group. Examples of such compounds include(3-acrylamidopropyl)trimethylammonium chloride, 3-methacrylamidopropyltrimethyl ammonium chloride, (ar-vinylbenzyl) trimethylammoniumchloride, (2-(methacryloyloxy)ethyl)trimethylammonium chloride,[3-(methacryloylamino)propyl]trimethyl ammonium chloride,(2-acrylamido-2-methylpropyl) trimethylammonium chloride,3-acrylamido-3-methylbutyl trimethyl ammonium chloride,acryloylamino-2-hydroxypropyl trimethyl ammonium chloride,N-(2-aminoethyl)acrylamide trimethyl ammonium chloride and mixturescomprising two or more thereof.

When the crosslinker has a solubility of below 2 wt % in a 10 wt % LiNO₃solution in water at 20° C., the total wt % of components (i)+(ii)relative to the total weight of the composition is preferably 30 to 90wt %, more preferably 30 to 88 or 90 wt %, especially 35 to 80 wt %,more especially 40 to 80 wt %, e.g. about 50 wt % or about 55 wt %.

When the crosslinker has a solubility of at least 2 wt % in a 10 wt %LiNO₃ solution in water at 20° C., the total wt % of components (i)+(ii)is preferably 40 to 85 wt %, more preferably 45 to 80 wt %, especially55 to 80 wt %, e.g. about 60 wt % or about 65 wt %. If one wishes toavoid swelling of the membrane and lower permselectivity the total wt %of components (i)+(ii) is preferably above 30 wt %.

The curable composition may comprise one or more than one crosslinker ascomponent (i). In this case, the abovementioned solubilities refer tothe solubility of the overall mixture of crosslinkers. In a particularlypreferred embodiment component (i) consists of crosslinking agent(s)having two acrylamide groups and component (ii) consists of curableionic compound(s) having one ethylenically unsaturated group and one ormore cationic group(s). Preferably the ethylenically unsaturated groupin component (ii) is a (meth)acrylamide group because this can result inmembranes having particularly good resistance to hydrolysis. The mostpreferred curable ionic compound is 3-acrylamidopropyl trimethylammoniumchloride.

Generally component (i) provides resistance to swelling for themembrane, while potentially reducing flexibility.

When component (ii) has only one ethylenically unsaturated group (e.g.one H₂C═CHCON<group) it is unable to crosslink. However it is able toreact with component (i). Component (ii) with only one ethylenicallyunsaturated can provide the resultant membrane with a desirable degreeof flexibility, which is particularly useful in applications requiringtightly wound membranes. Component (ii) also assists the membrane indistinguishing between ions of different charges by providing cationicgroups.

In one embodiment the composition comprises less than 10 wt %, morepreferably less than 5 wt %, of ethylenically unsaturated compoundsother than components (i) and (ii). In a preferred embodiment thecomposition is free from ethylenically unsaturated compounds other thancomponents (i) and (ii).

The solvent content of the composition is preferably the minimum, orless than 5% more than the minimum, necessary to achieve the compositionin the form of a homogeneous solution, while at the same time being atleast 15 wt %.

Polar solvents, especially aqueous solvents, are preferred because theseare particularly good at dissolving the curable ionic compound.Preferably at least half of the solvent is water, with the balancecomprising organic solvent. The organic solvent can be useful forproviding a homogenous solution of all the components of thecomposition. The inclusion of an organic solvent may also haveadvantages in the process for preparing the membrane because manyorganic solvents will usefully reduce the viscosity and/or surfacetension of the composition, making the manufacturing process easier insome respects. Preferably the solvent comprises at least 40 wt % water,more preferably at least 60 wt % water. Preferably the compositioncomprises 15 to 55 wt %, more preferably 16 to 45 wt %, especially 20 to40 wt % and more especially 22 to 35 wt % solvent.

The solvent is preferable water or a mixture comprising water and awater-miscible organic solvent. Due to the presence of a water-miscibleorganic solvent, water-immiscible solvents may also be tolerated insmall amounts such that the overall solvent mixture is miscible.

When the solvent comprises water and an organic solvent the weight ratioof water:organic solvent is preferably higher than 2:3, more preferablybetween 10:1 and 1:1, more preferably between 10:1 and 1:2, especiallybetween 5:1 and 1:1 and more especially between 3:1 and 2:1.

The organic solvent is optionally a single organic solvent or acombination of two or more organic solvents.

Preferred organic solvents include C₁₋₄ alcohols (e.g. methanol, ethanoland propan-2-ol), diols (e.g. ethylene glycol and propylene glycol),triols (e.g. glycerol), carbonates (e.g. ethylene carbonate, propylenecarbonate, dimethyl carbonate, diethyl carbonate, di-t-butyl dicarbonateand glycerin carbonate), dimethyl formamide, acetone,N-methyl-2-pyrrolidinone and mixtures comprising two or more thereof. Aparticularly preferred organic solvent is propan-2-ol.

In one embodiment the organic solvent has a low boiling point e.g. aboiling point below 100° C. Solvents having a low boiling point can beeasily removed by evaporation, avoiding the need for a washing step forremoval of the solvent.

The optimum solvent content for the curable composition depends to someextent on the interaction between the solvent, the curable compound(s)and the crosslinker, and can be determined for each combination bysimple experimentation.

When the composition contains 0% free radical initiator it may be curedusing electron beam radiation.

Preferably the composition comprises 0.01 to 10 wt %, more preferably0.01 to 5 wt %, especially 0.01 to 2 wt %, more especially 0.05 to 2 wt% free radical initiator. The preferred free radical initiator is aphotoinitiator.

The curable composition may comprise one or more than one free radicalinitiator as component (iv).

For acrylamides, diacrylamides, and higher-acrylamides, type Iphotoinitiators are preferred. Examples of type I photoinitiators are asdescribed in WO 2007/018425, page 14, line 23 to page 15, line 26, whichare incorporated herein by reference thereto. Especially preferredphotoinitiators include alpha-hydroxyalkylphenones, e.g.2-hydroxy-2-methyl-1-phenyl propan-1-one and2-hydroxy-2-methyl-1-(4-tert-butyl-) phenylpropan-1-one, andacylphosphine oxides, e.g. 2,4,6-trimethylbenzoyl-diphenylphosphineoxide, and bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide.

The curable composition optionally contains (vi) 0 to 10 wt %,preferably 0 to 5 wt %, of curable compound(s) other than (i) which havemore than one ethylenically unsaturated group and no ionic groups.

The curable composition optionally contains (vii) 0 to 20 wt %,preferably 0 to 10 wt %, of curable compound(s) having one ethylenicallyunsaturated group and no ionic groups.

When a radical initiator is present in the composition, preferably apolymerization inhibitor is also included. This is useful to preventpremature curing of the composition during, for example, storage.Suitable inhibitors include hydroquinone, hydroquinone mono methylether, 2,6-di-t-butyl-4-methylphenol, 4-t-butyl-catechol, phenothiazine,4-oxo-2,2,6,6-tetramethyl-1-piperidinoloxy, free radical,4-hydroxy-2,2,6,6-tetramethyl-1-piperidinoloxy, free radical,2,6-dinitro-sec-butylphenol, tris(N-nitroso-N-phenylhydroxylamine)aluminum salt, Omnistab™ IN 510 and mixtures comprising two or morethereof.

The curable composition may contain other components, for example acids,pH controllers, preservatives, viscosity modifiers, stabilisers,dispersing agents, antifoam agents, organic/inorganic salts, anionic,cationic, non-ionic and/or amphoteric surfactants, buffers and the like.

A buffer may be used to reduce fluctuations in pH value caused byvariation in concentrations of acidic and basic compounds.

The curable composition may of course contain further components notspecifically mentioned or excluded above.

Curing rates may be increased by including an amine synergist in thecurable composition. Suitable amine synergists are, for example, freealkyl amines, e.g. triethylamine or triethanol amine; aromatic amines,e.g. 2-ethylhexyl-4-dimethylaminobenzoate, ethyl-4-dimethylaminobenzoateand also polymeric amines as polyallylamine and its derivatives.

Curable amine synergists such as ethylenically unsaturated amines (e.g.acrylated amines) are preferable since their use will give less odourdue to their ability to be incorporated into the membrane by curing andalso because they may contain a basic group which can be useful in thefinal (anion permeable) membrane.

When used the amount of amine synergists is preferably from 0.1 to 10wt. % based on the total weight of polymerisable components in thecomposition, more preferably from 0.3 to 3 wt %.

In view of the foregoing a particularly preferred composition comprisesa curable composition comprising:

-   (i) 4 to 35 wt % crosslinker comprising at least two acrylamide    groups;-   (ii) 35 to 60 wt % curable ionic compound comprising an    ethylenically unsaturated group and an cationic group; and-   (iii) 16 to 45 wt % solvent;-   (iv) 0.01 to 2 wt % of photoinitiator;-   (v) 2 to 30 wt % of non-curable salt;    wherein the molar ratio of (i):(ii) is at least 0.15 and preferably    below 1.5. More preferably the molar ratio of (i):(ii) is between    0.2 and 1.0.

In an alternative embodiment the curable composition comprising:

-   (i) 5 to 35 wt % crosslinker comprising at least two acrylamide    groups;-   (ii) 20 to 65 wt % curable ionic compound comprising an    ethylenically unsaturated group and an cationic group; and-   (iii) 16 to 45 wt % solvent;-   (iv) 0.01 to 2 wt % of photoinitiator;-   (v) 3 to 40 wt % of non-curable salt;    wherein the molar ratio of (i):(ii) is between 0.10 and 5.    Preferably the molar ratio of (i):(ii) is between 0.15 and 1.5; more    preferably the molar ratio of (i):(ii) is between 0.2 and 1.0.

The optimum amounts of all components depends to some extent on theproperties of the individual components selected and on the intended useof the composition.

Preferably this composition has a pH of 1.5 to 11.

Preferably the ethylenically unsaturated group is an (meth)acrylamidegroup.

Preferably the number of parts of (i), (ii), (iii), (iv) and (v) in theaforementioned curable compositions add up to 100. This does not ruleout the presence of further, different components, but merely sets theratio of the mentioned components relative to the total mount of suchcomponents.

Preferably the curable composition is free from, or substantially freefrom, methacrylic compounds (e.g. methacrylate and methacrylamidecompounds), i.e. the composition comprises at most 10 wt % of compoundswhich are free from acrylic groups and comprise one or more methacrylicgroups.

Preferably the curable composition is free from, or substantially freefrom, divinyl benzene.

Preferably the curable composition is free from, or substantially freefrom, styrene.

Preferably the curable composition is free from, or substantially freefrom, dyes and pigments. This is because there is no need to includedyes or pigments in the composition.

Thus the preferred curable composition is free from, or substantiallyfree from, divinyl benzene, dyes, pigments, styrene, methacryliccompounds and compounds having sulpho groups.

According to a second aspect of the present invention there is provideda process for preparing a membrane comprising the following steps:

-   (i) applying a curable composition to a support; and-   (ii) curing the composition to form a membrane;    wherein the curable composition is as defined in the first aspect of    the present invention.

Hitherto such membranes have often been made in slow and energyintensive processes, often having many stages. The present inventionenables the manufacture of membranes in a simple process that may be runcontinuously for long periods of time to mass produce membranesrelatively cheaply.

Optionally the process comprises the further step of separating thecured composition and support. However if desired this further step maybe omitted and thereby a composite membrane is produced comprising thecured composition and a porous support.

The membrane is preferably a cation exchange membrane.

The thickness of the membrane, including the support, is preferably lessthan 250 μm, more preferably between 10 and 200 μm, most preferablybetween 20 and 150 μm.

Preferably the membrane has an ion exchange capacity of at least 0.1meq/g, more preferably of at least 0.3 meq/g, especially more than 0.6meq/g, more especially more than 1.0 meq/g, based on the total dryweight of the membrane and any porous support and any porousstrengthening material which remains in contact with the resultantmembrane. Ion exchange capacity may be measured by titration asdescribed by Djugolecki et al, J. of Membrane Science, 319 (2008) onpage 217.

Preferably the membrane has a permselectivity for small anions (e.g.Cl⁻) of more than 80%, especially more than 85% or more especially morethan 90%, e.g. more than 95%.

Preferably the membrane has an electrical resistance less than 10ohm·cm², more preferably less than 5 ohm·cm², most preferably less than3 ohm·cm². For certain applications a high electrical resistance may beacceptable especially when the permselectivity is very high, e.g. 90% orhigher. The electrical resistance may be determined by the methoddescribed below in the examples section.

Preferably the membrane exhibits a swelling in water of less than 100%,more preferably less than 75%, most preferably less than 60%. The degreeof swelling can be controlled by the amount of crosslinker, the amountof non-curable salts and by selecting appropriate parameters in thecuring step and further by the properties of the porous support.

Electrical resistance, permselectivity and % swelling in water may bemeasured by the methods described by Djugolecki et al, J. of MembraneScience, 319 (2008) on pages 217-218.

Typically the ion exchange membrane is substantially non-porous e.g. thepores are smaller than the detection limit of a standard ScanningElectron Microscope (SEM). Thus using a Jeol JSM-6335F Field EmissionSEM (applying an accelerating voltage of 2 kV, working distance 4 mm,aperture 4, sample coated with Pt with a thickness of 1.5 nm,magnification 100,000×, 3° tilted view) the average pore size isgenerally smaller than 5 nm, preferably smaller than 2 nm.

The resultant membrane preferably has a low water permeability so thations may pass through the membrane and water molecules do not pasthrough the membrane. Preferably the membrane's water permeability islower than 1.10⁻⁷ m³/m²·s·kPa, more preferably lower than 1.10⁻⁸m³/m²·s·kPa, most preferably lower than 5.10⁻⁹ m³/m²·s·kPa, especiallylower than 1.10⁻⁹ m³/m²·s·kPa. The requirements for water permeabilitydepend on the intended use of the membrane.

Where desired, a surfactant or combination of surfactants may beincluded in the composition as a wetting agent or to adjust surfacetension. Commercially available surfactants may be utilized, includingradiation-curable surfactants. Surfactants suitable for use in thecomposition include non-ionic surfactants, ionic surfactants, amphotericsurfactants and combinations thereof.

Preferably the components of the curable composition are selected suchthat no phase separation occurs during the curing step. In this way, thelikelihood of a macro porous structure in the resultant membrane isreduced.

The network structure of the membrane is determined to some extent bythe identity of the crosslinking agent(s) and the curable compound andtheir functionality, e.g. the number of crosslinkable groups theycontain per molecule.

During the curing process, the curable composition may form a layer ontop of the support, or it may permeate wholly or partially into thepores of the support and thus forming an impregnated composite membrane.The curable composition may also be applied to both sides of the supportto achieve a symmetrical composite membrane. In a preferred embodimentthe support is saturated with the composition and the saturated supportis cured by EB or UV irradiation.

The process of the present invention may contain further steps ifdesired, for example washing and/or drying the resultant membrane.

Before applying the curable composition to the surface of the support,the support may be subjected to a corona discharge treatment, plasmaglow discharge treatment, flame treatment, ultraviolet light irradiationtreatment, chemical treatment or the like, e.g. for the purpose ofimproving its wettability and the adhesiveness.

The support may also be treated to modify its surface energy, e.g. tovalues above 70 mN/m.

While it is possible to prepare the membrane on a batch basis using astationary support, to gain full advantage of the invention it is muchpreferred to prepare the membrane on a continuous basis using a movingsupport. The support may be in the form of a roll which is unwoundcontinuously or the support may rest on a continuously driven belt (or acombination of these methods). Using such techniques the curablecomposition can be applied to the support on a continuous basis or itcan be applied on a large batch basis.

The curable composition may be applied to the support by any suitablemethod, for example by curtain coating, blade coating, air-knifecoating, knife-over-roll coating, slide coating, nip roll coating,forward roll coating, reverse roll coating, micro-roll coating, dipcoating, foulard coating, kiss coating, rod bar coating or spraycoating. The coating of multiple layers can be done simultaneously orconsecutively. When coating multiple layers the curable compositions maybe the same of different. For simultaneous coating of multiple layers,curtain coating, slide coating and slot die coating are preferred. Thecurable composition may be applied to one side of the support or to bothsides of the support.

In one embodiment at least two of the curable compositions, which may bethe same or different, are applied to the support, e.g. simultaneouslyor consecutively. The curable compositions may be applied to the sameside of the support or to different sides. Thus the application step maybe performed more than once, either with or without curing beingperformed between each application. When applied to different sides theresultant composite membrane may be symmetrical or asymmetrical and thelayers of curable composition may have the same or differentthicknesses. When applied to the same side a composite membrane may beformed comprising at least one top layer and at least one bottom layerthat is closer to the support than the top layer. In this embodiment thetop layer and bottom layer, together with any intervening layers,constitute the membrane and the porous support provides strength to theresultant composite membrane.

Thus in a preferred process, the curable composition is appliedcontinuously to a moving support, more preferably by means of amanufacturing unit comprising one or more curable compositionapplication stations, one or more irradiation sources for curing thecomposition, a membrane collecting station and a means for moving thesupport from the curable composition application station to theirradiation source and to the membrane collecting station.

The curable composition application station(s) may be located at anupstream position relative to the irradiation source(s) and theirradiation source(s) is/are located at a an upstream position relativeto the membrane collecting station.

In order to produce a sufficiently flowable curable composition forapplication by a high speed coating machine, it is preferred that thecurable composition has a viscosity below 5000 mPa·s when measured at35° C., more preferably from 1 to 1500 mPa·s when measured at 35° C.Most preferably the viscosity of the curable composition is from 2 to500 mPa·s when measured at 35° C. For coating methods such as slide beadcoating the preferred viscosity is from 2 to 150 mPa·s when measured at35° C.

With suitable coating techniques, the curable composition may be appliedto a support moving at a speed of over 5 m/min, preferably over 10m/min, more preferably over 15 m/min, e.g. more than 20 m/min, or evenhigher speeds, such as 60 m/min, 120 m/min or up to 400 m/min can bereached.

Curing is preferably performed by radical polymerisation, preferablyusing electromagnetic radiation. The source of radiation may be anysource which provides the wavelength and intensity of radiationnecessary to cure the composition. A typical example of a UV lightsource for curing is an D-bulb with an output of 600 Watts/inch (240W/cm) as supplied by Fusion UV Systems. Alternatives are the V-bulb andthe H-bulb from the same supplier.

When no photo-initiator is included in the curable composition, thecomposition can be cured by electron-beam exposure, e.g. using anexposure of 50 to 300 keV. Curing can also be achieved by plasma orcorona exposure

During curing the components (i) and (ii) polymerise to form a polymericmembrane. The curing may be brought about by any suitable means, e.g. byirradiation and/or heating. Preferably curing occurs sufficientlyrapidly to form a membrane within 30 seconds. If desired further curingmay be applied subsequently to finish off, although generally this isnot necessary.

The curing is preferably achieved thermally (e.g. by irradiating withinfrared light) or, more preferably, by irradiating the composition withultraviolet light or an electron beam.

For thermal curing the curable composition preferably comprises one ormore thermally reactive free radical initiators, preferably beingpresent in an amount of 0.01 to 5 parts per 100 parts of curablecomposition, wherein all parts are by weight.

Examples of thermally reactive free radical initiators include organicperoxides, e.g. ethyl peroxide and/or benzyl peroxide; hydroperoxides,e.g. methyl hydroperoxide, acyloins, e.g. benzoin; certain azocompounds, e.g. α,α′-azobisisobutyronitrile and/orγ,γ′-azobis(γ-cyanovaleric acid); persulfates; peracetates, e.g. methylperacetate and/or tert-butyl peracetate; peroxalates, e.g. dimethylperoxalate and/or di(tert-butyl) peroxalate; disulfides, e.g. dimethylthiuram disulfide and ketone peroxides, e.g. methyl ethyl ketoneperoxide. Temperatures in the range of from about 30° C. to about 150°C. are generally employed for infrared curing. More often, temperaturesin the range of from about 40° C. to about 110° C. are used.

Preferably curing of the curable composition begins within 3 minutes,more preferably within 60 seconds, after the composition has beenapplied to the support.

Preferably the curing is achieved by irradiating the curable compositionfor less than 30 seconds, more preferably less than 10 seconds,especially less than 3 seconds, more especially less than 2 seconds. Ina continuous process the irradiation occurs continuously and the speedat which the curable composition moves through the beam of irradiationis mainly what determines the time period of curing.

Preferably the curing uses ultraviolet light. Suitable wavelengths arefor instance UV-A (390 to 320 nm), UV-B (320 to 280 nm), UV-C (280 to200 nm) and UV-V (445 to 395 nm), provided the wavelength matches withthe absorbing wavelength of any photo-initiator included in the curablecomposition.

Suitable sources of ultraviolet light are mercury arc lamps, carbon arclamps, low pressure mercury lamps, medium pressure mercury lamps, highpressure mercury lamps, swirlflow plasma arc lamps, metal halide lamps,xenon lamps, tungsten lamps, halogen lamps, lasers and ultraviolet lightemitting diodes. Particularly preferred are ultraviolet light emittinglamps of the medium or high pressure mercury vapour type. In most caseslamps with emission maxima between 200 and 450 nm are particularlysuitable.

The energy output of the irradiation source is preferably from 20 to1000 W/cm, preferably from 40 to 500 W/cm but may be higher or lower aslong as the desired exposure dose can be realized. The exposureintensity is one of the parameters that can be used to control theextent of curing which influences the final structure of the membrane.Preferably the exposure dose is at least 40 mJ/cm², more preferablybetween 40 and 1500 mJ/cm², most preferably between 70 and 900 mJ/cm² asmeasured by an High Energy UV Radiometer (UV PowerMap™ from EIT, Inc) inthe UV-A and UV-B range indicated by the apparatus. Exposure times canbe chosen freely but preferably are short and are typically less than 10seconds, more preferably less than 5 seconds, especially less than 3seconds, more especially less than 2 seconds, e.g. between 0.1 and 1second.

To reach the desired exposure dose at high coating speeds, more than oneUV lamp may be used, so that the curable composition is irradiated morethan once. When two or more lamps are used, all lamps may give an equaldose or each lamp may have an individual setting. For instance the firstlamp may give a higher dose than the second and following lamps or theexposure intensity of the first lamp may be lower. Varying the exposuredose of each lamp may influence the polymer matrix structure and thefinal crosslink density. In a preferred embodiment the composition iscured by simultaneous irradiation from opposite sides using two or moreirradiation sources, e.g. two lamps (one at each side). The two or moreirradiation sources preferably irradiate the composition with the sameintensity. By using this symmetric configuration, a higher crosslinkingefficiency can be achieved and curling of the membrane can be reduced orprevented.

Photoinitiators may be included in the curable composition, as mentionedabove, and are usually required when curing uses UV or visible lightradiation. Suitable photoinitiators are those known in the art. Curingby irradiation with UV or electron beam is preferably performed atbetween 20 and 60° C. While higher temperatures may be used, these arenot preferred because they can lead to higher manufacturing costs.

Preferred supports are porous, e.g. they may be a woven or non-wovensynthetic fabric, e.g. polyethylene, polypropylene, polyacrylonitrile,polyvinyl chloride, polyester, polyamide, and copolymers thereof, orporous membranes based on e.g. polysulfone, polyethersulfone,polyphenylenesulfone, polyphenylenesulfide, polyimide, polyethermide,polyamide, polyamideimide, polyacrylonitrile, polycarbonate,polyacrylate, cellulose acetate, polypropylene, poly(4-methyl1-pentene), polyinylidene fluoride, polytetrafluoroethylene,polyhexafluoropropylene, polychlorotrifluoroethylene, and copolymersthereof.

Various porous supports are available commercially, e.g. fromFreudenberg Filtration Technologies (Novatexx materials) and Sefar AG.

Surprisingly, ion exchange membranes with cationic groups can exhibitgood properties in terms of their permselectivity and conductivity whileat the same time being not overly expensive to manufacture by thepresent process.

The present process allows the preparation of membranes having adesirable degree of flexibility, without being overly flexible or toorigid. The presence of the solvent improves coatability for the curablecomposition and can provide thin membranes with low numbers of defects,low tendency to curl while retaining good durability in use.

According to a third aspect of the present invention there is provided amembrane obtained by a process according to the second aspect of thepresent invention.

The membranes according to the third aspect of the present invention mayalso be put to other uses requiring membranes having cationic groups.

The membranes according to the third aspect of the present inventionpreferably have the properties described above in relation to the secondaspect of the present invention.

The membranes of the invention are particularly useful for ED, (C)EDI,EDR, ZDD, FTC, DD, EL and RED, although they may also be used for otherpurposes (e.g. pervaporation, fuel cells).

According to a fourth aspect of the present invention there is provideduse of a membrane according to the third aspect of the present inventionfor water purification or for the generation of electricity.

According to a fourth aspect of the present invention there is providedan electrodialysis or reverse electrodialysis unit, anelectrodeionization module or a flow through capacitor comprising one ormore membranes according to the third aspect of the present invention.The electrodeionization module is preferably a continuouselectrodeionization module.

Preferably the electrodialysis or reverse electrodialysis unit or theelectrodeionization module or the flow through capacitor comprises atleast one anode, at least one cathode and one or more membrane accordingto the third aspect of the present invention. Further the unitpreferably comprises an inlet for providing a flow of relatively saltywater along a first side of a membrane according to the presentinvention and an inlet for providing a less salty flow water along asecond side of the membrane such that ions pass from the first side tothe second side of the membrane. Preferably the one or more membranes ofthe unit comprise a membrane according to the third aspect of thepresent invention having cationic groups and a further membrane havinganionic groups.

In a preferred embodiment the unit comprises at least 3, more preferablyat least 5, e.g. 36, 64 or up to 500, membranes according to the thirdaspect of the present invention, the number of membranes being dependenton the application. The membrane may for instance be used in aplate-and-frame or stacked-disk configuration or in a spiral-wounddesign. Alternatively, a continuous first membrane according to thepresent invention having cationic groups may be folded in a concertina(or zigzag) manner and a second membrane having anionic groups (i.e. ofopposite charge to the first membrane) may be inserted between the foldsto form a plurality of channels along which fluid may pass and havingalternate anionic and cationic membranes as side walls.

The invention will now be illustrated with non-limiting examples whereall parts and percentages are by weight unless specified otherwise.

In the examples the following properties were measured by the methodsdescribed below.

GENERAL TEST METHODS

Permselectivity was measured by using a static membrane potentialmeasurement. Two cells are separated by the membrane underinvestigation. Prior to the measurement the membrane was equilibrated ina 0.1 M NaCl solution for at least 12 hours. Two streams havingdifferent NaCl concentrations were passed through cells on oppositesides of the membranes under investigation. One stream had aconcentration of 0.1M NaCl (from Sigma Aldrich, min. 99.5% purity) andthe other stream was 0.5 M NaCl. The flow rate of both streams was 0.90dm³/min. Two Calomel reference electrodes (from Metrohm AG, Switzerland)were connected to Haber-Luggin capillary tubes that were inserted ineach cell and were used to measure the potential difference over themembrane. The effective membrane area was 3.14 cm² and the temperaturewas 25° C.

When a steady state was reached, the membrane potential was measured(ΔV_(meas))

The permselectivity (α (%)) of the membrane was calculated according theformula:

α(%)=ΔV _(meas) /ΔV _(theor)*100%.

The theoretical membrane potential (ΔV_(theor)) is the potential for a100% permselective membrane as calculated using the Nernst equation. Tocompensate for day-to-day measurement fluctuations, all a (%)measurements included an internal standard to normalize the results. Theinternal standard used was AMX membrane from Tokuyama Soda having an α(%) value of 92%.

Electrical resistance (“ER”) was measured by the method described byDjugolecki et al, J. of Membrane Science, 319 (2008) on page 217-218with the following modifications:

-   -   the auxiliary membranes were CMX and AMX from Tokuyama Soda,        Japan;    -   double headed peristaltic pumps from Watson Marlow (type 504        S/50) were used for the four outer compartments and a Cole        Parmer masterflex console drive (77521-47) with easy load II        model 77200-62 gear pumps for the two central compartments;    -   the flowrate of each stream was 475 ml/min controlled by Porter        Instrument flowmeters (type 150AV-B250-4RVS) and Cole Parmer        flowmeters (type G-30217-90);    -   the effective area of the membrane was 3.14 cm².

Ingredients

MBA is N,N′-methylene bisacrylamide (MW=154) from Sigma Aldrich.

BAHP is 1,4-bis(acryloyl) homopiperazine, synthesized as described in WO2010/106356

ATMAC is 3-acrylamidopropyl-trimethylammonium chloride from Kohjin

HDMAP is 2-hydroxy-2-methyl-1-phenyl-propan-1-one, a photoinitiator fromCytec.

MeHQ is hydroquinone monomethyl ether, a polymerisation inhibitor fromMerck

IPA is 2-propanol from Shell.

MeOH and EtOH are methanol and ethanol (96%) respectively from SigmaAldrich.

LiNO₃, LiBr and LiCl are lithium salts from Sigma Aldrich.

Novatexx™ 2597 is a nonwoven polyamide material from FreudenbergFiltration Technologies.

Novatexx™ 2426 is a nonwoven polyethyleneterephthalate material fromFreudenberg Filtration Technologies.

When calculating the solvent content, the amount of any solvents presentin any of the ingredients was included (e.g. any waters ofcrystallisation were treated as solvent).

EXAMPLES 1 TO 15 AND COMPARATIVE EXAMPLES 1 AND 2

Curable compositions CC1 to CC15 according to the invention andcomparative curable compositions CE1 and CE2 were prepared by mixing theingredients (expressed in wt %) shown in Table 1 at 80° C.,

TABLE 1 Ingredient CC1 CC2 CC3 CC4 CC5 CC6 CC7 CC8 CC9 CC10 ATMAC (ii)44.0 43.1 42.4 40.4 40.0 38.1 38.4 33.5 32.8 27.5 MBA (i) 5.1 6.3 6.88.8 9.9 10.6 10.6 12.5 15.8 16.7 BAHP (i) 0 0 0 0 0 0 0 0 0 0 HDMAP 1.01.0 1.0 1.0 0.7 1.0 1.0 0.9 0.9 0.8 Water* 30.7 30.0 29.4 28.5 20.6 27.627.7 24.9 25.3 30.8 IPA 0 0 0 0 8.4 0 0 0 0 0 LiBr 0 0 0 0 0 0 0 28.2 00 LiNO₃ 19.1 19.7 20.4 21.3 20.4 22.7 22.3 0 25.1 24.2 Molar ratio(i):(ii) 0.16 0.19 0.21 0.29 0.33 0.37 0.37 0.50 0.65 0.82 α (%) 86.286.5 89.9 89.5 88.0 88.0 91.0 90.6 90.0 87.4 ER 0.48 0.37 1.43 0.91 1.151.48 1.02 0.92 1.14 4.15 (ohm · cm²) Ingredient CC11 CC12 CC13 CC14 CC15CE1 CE2 ATMAC (ii) 28.0 24.8 21.1 17.8 13.6 45.5 8.8 MBA (i) 19.0 19.021.8 0 0 2.4 0 BAHP (i) 0 0 0 40.7 43.6 0 47.1 HDMAP 1.0 0.8 0.8 1.7 1.91.3 2.0 Water* 24.0 29.7 29.0 36.4 37.3 33.0 38.2 LiNO₃ 28.0 25.7 27.33.4 3.6 17.8 3.9 Molar ratio (i):(ii) 0.91 1.03 1.39 2.27 3.19 0.07 5.32α (%) 89.2 86.5 86.4 90.0 90.6 79.9 86.0 ER (ohm · cm²) 1.40 2.41 3.177.93 9.47 0.27 13.6 *The water included MeHQ polymerization inhibitor(ca. 1000 ppm).

The curable compositions were applied to applied to an aluminiumunderground carrier using a 150 μm wire wound bar, at a speed ofapproximately 5 m/min by hand, followed by application of a non-wovensupport (Novatexx™ 2597) levelled using a wire wound rod coater to athickness of 4 micrometers. The temperature of the curable compositionswas 50° C. A membrane was prepared by curing the coated support using aLight Hammer LH6 from Fusion UV Systems fitted with a D-bulb working at100% intensity with a speed of 30 m/min (single pass). The exposure timewas 0.47 seconds. After curing, the membrane was stored in a 0.1 M NaClsolution for at least 12 hours.

The permselectivity (α (%)) and electrical resistivity (ER) of theresultant membranes were as shown in Table 1.

EXAMPLES 16 TO 19

Curable compositions CC16 to CC19 according to the invention wereprepared by mixing the ingredients shown in an analogous manner toExamples 1 to 15 using the ingredients listed in Table 2.

TABLE 2 Ingredient CC16 CC17 CC18 CC19 ATMAC (ii) 31 26 26 26 MBA (i) 2118 18 18 HDMAP 1.0 1.0 1.0 1.0 Water 28 28 28 28 IPA 0 10 0 0 MeOH 0 010 0 EtOH 0 0 0 10 LiCl 19 17 17 17 Molar ratio (i):(ii) 0.91 0.93 0.930.93 α (%) 89.4 89.4 88.8 88.8 ER (ohm · cm2) 1.5 1.7 1.5 1.2 * Thewater included MeHQ polymerization inhibitor (ca. 1000 ppm).

CC16 to CC19 were applied to Novatexx™ 2426 support by the methoddescribed in Example 1.

The permselectivity (α (%)) and electrical resistivity (ER) of theresultant membranes were as shown above in Table 2.

1. A membrane obtained from a process comprising the following steps:(i) applying a curable composition to a support; and (ii) curing thecomposition to form a membrane; wherein the curable compositioncomprises: (i) 2.5 to 50 wt % crosslinker comprising at least twoacrylamide groups; (ii) 12 to 65 wt % curable ionic compound comprisingan ethylenically unsaturated group and a cationic group; (iii) 10 to 70wt % solvent; (iv) 0 to 10 wt % of free radical initiator; and (v)non-curable salt comprising a cation and an anion, wherein the anion isnot sulfate; wherein the molar ratio of (i):(ii) is greater than 0.10.2. The membrane according to claim 1 wherein the molar ratio of (i):(ii)is less than
 5. 3. The membrane according to claim 1 wherein the totalwt % of components (i) and (ii) relative to the total weight of thecomposition is 30 to 88 wt %.
 4. The membrane according to claim 1comprising 2 to 50 wt % of non-curable salt as component (v).
 5. Themembrane according to claim 1 wherein the molar ratio of (i):(ii) is atleast 0.15 and which comprises 20 to 65 wt % of component (ii).
 6. Themembrane according to claim 1 wherein the solvent comprises water and awater-miscible organic solvent.
 7. The membrane according to claim 1which comprises 0.005 to 10 wt % photoinitiator as component (iv). 8.The membrane according to claim 1 which is free from ethylenicallyunsaturated compounds other than components (i) and (ii).
 9. Themembrane according to claim 1 wherein the ethylenically unsaturatedgroup is an acrylamide or a methacrylamide group.
 10. The membraneaccording to claim 1 wherein the composition comprises: (i) 5 to 35 wt %crosslinker comprising at least two acrylamide groups; (ii) 20 to 65 wt% curable ionic compound comprising an ethylenically unsaturated groupand a cationic group; and (iii) 16 to 45 wt % solvent; (iv) 0.01 to 2 wt% of photoinitiator; and (v) 3 to 40 wt % of non-curable salt comprisinga cation and an anion, wherein the anion is not sulfate; wherein themolar ratio of (i):(ii) is at least 0.15.
 11. The membrane according toclaim 1 wherein the molar ratio of (i):(ii) is at least 0.15 and lessthan 1.5.
 12. The membrane according to claim 1 wherein the compositionis cured by irradiation with an electron beam or UV light for a periodof less than 30 seconds.
 13. The membrane according to claim 1 whereinthe curable composition is applied continuously to a moving supportusing a manufacturing unit comprising a curable composition applicationstation, an irradiation source for curing the composition, and amembrane collecting station and wherein the support moves from thecurable composition application station to the irradiation source and tothe membrane collecting station.
 14. The membrane according to claim 10wherein the molar ratio of (i):(ii) is less than 1.5.
 15. Anelectrodialysis or reverse electrodialysis unit, a flow throughcapacitor device, a fuel cell, a diffusion dialysis apparatus or amembrane electrode assembly comprising one or more membranes accordingto claim
 1. 16. An electrodialysis or reverse electrodialysis unit, aflow through capacitor device, a fuel cell, a diffusion dialysisapparatus or a membrane electrode assembly comprising one or moremembranes according to claim
 9. 17. An electrodialysis or reverseelectrodialysis unit, a flow through capacitor device, a fuel cell, adiffusion dialysis apparatus or a membrane electrode assembly comprisingone or more membranes according to claim
 10. 18. An electrodialysis orreverse electrodialysis unit, a flow through capacitor device, a fuelcell, a diffusion dialysis apparatus or a membrane electrode assemblycomprising one or more membranes according to claim
 11. 19. Anelectrodialysis or reverse electrodialysis unit comprising one or moremembranes according to claim
 1. 20. An electrodialysis or reverseelectrodialysis unit comprising one or more membranes according to claim10.